FIG. 1 illustrates the structure of radio interface protocol uplink layer 2 of an E-UTRAN (evolved universal terrestrial radio access network) in a third-generation mobile communications LTE (long term evolution) system.
On a MAC (media access control) protocol layer, there is scheduling/priority handling functional entities, wherein the scheduling function supports dynamic scheduling and semi-persistent scheduling (or known as semi-static scheduling); and the priority handling function supports priority handling between different logical channels of one UE (user equipment) as well as priority handling between different UEs through dynamic scheduling.
Uplink dynamic scheduling function refers to that, on uplink, through a C-RNTI (cell radio network temporary identifier) on L1/L2 (layer 1/layer 2) control channel, the E-UTRAN is capable of allocating resources, such as PRBs (physical resource blocks) and an MCS (modulation and coding scheme), for a UE at each TTI (transmit time interval). When downlink reception is allowed (controlled by DRX (discontinuous reception function)), the UE always monitors the L1/L2 control channel to find possible resource allocation for uplink transmission. Herein the L1/L2 control channel refers to a PDCCH (physical downlink control channel), which is mainly used for carrying UL grant during uplink scheduling. During the uplink scheduling, the UE carries an SR (scheduling request) and a CQI (channel quality indicator) on a PUCCH (physical uplink control channel), and uplink data is transmitted on a PUSCH (physical uplink shared channel). With respect to uplink transmission of the UE, the E-UTRAN feeds back an acknowledgement/negative-acknowledgement message (ACK/NACK) in response to a hybrid ARQ (automatic repeat request) through a PHICH (physical hybrid ARQ indicator channel).
Uplink semi-persistent scheduling refers to that, the E-UTRAN may allocate predefined uplink resources, such as timing, resource, transport format and the like, for a first time HARQ (hybrid ARQ) transmission of the UE. During sub-frames in which resources are pre-allocated for the UE, the UE performs uplink transmission according to the predefined resources at corresponding TTI if the UE does not discover its C-RNTI on the L1/L2 control channel. A network decodes predefined PRB according to predefined MCS. In addition, During sub-frames in which resources are pre-allocated for the UE, the UE performs uplink transmission according to information indicated by the L1/L2 control channel at corresponding TTI if the UE discovers its C-RNTI on the L1/L2 control channel, that is, the allocation of the L1/L2 control channel overrides the predefined allocation at corresponding TTI, namely, at the corresponding TTI, the dynamic scheduling may cover the semi-persistent scheduling.
In general, the retransmission of the HARQ uses the dynamic scheduling; also maybe use the semi-persistent scheduling. Typically, the semi-persistent scheduling is applied to VoIP service. Initial configuration of the semi-persistent scheduling, such as semi-persistent scheduling periodicity (or called semi-persistent scheduling interval), is performed by an RRC (radio resource control) signaling. Activation of the semi-persistent scheduling is controlled by the PDCCH, and the PDCCH indicates whether the UL grant is semi-persistent or dynamic by a certain mechanism, for example, by a special C-RNTI different from that used for the dynamic scheduling. Generally, a UE allocated with predefined semi-persistent resource no longer needs to transmit a scheduling request through the PUCCH. For the retransmission of the HARQ by dynamic scheduling or semi-persistent scheduling, both adaptive retransmission and non-adaptive retransmission can be used. The time difference between the initial transmission of the HARQ and the retransmission of the HARQ is referred to as an HARQ RTT (Round-Trip Time).
For uplink semi-persistent scheduling transmission, as synchronous HARQ technology is adopted, in the process of the semi-persistent scheduling, in the case that the least common multiple of the semi-persistent scheduling periodicity and the HARQ RTT is too small, that is, the timing collision interval between the retransmission of the HARQ and the semi-persistent scheduling is too small, an extra PDCCH signaling is required for scheduling. For example, in an LTE TDD (time division duplex) system, a typical HARQ RTT of uplink scheduling transmission in the LTE TDD system is 10 ms, while a data arrival interval for the VoIP (voice over internet protocol) service of the semi-persistent scheduling is 20 ms, the semi-persistent scheduling periodicity is also generally set to be 20 ms, which is just two times the HARQ RTT, so the least common multiple of the semi-persistent scheduling periodicity and the HARQ RTT is 20 ms, that is, the timing collision interval between the retransmission of the HARQ and the semi-persistent scheduling is 20 ms. As shown in FIG. 2, the boxes with horizontal stripes represent sub-frames used for transmitting initial data packets of the HARQ, the boxes with vertical stripes represent sub-frames used for retransmission, in which each numeral represents a serial number of each HARQ data packet. When the HARQ packet of the second VoIP is transmitted for the first time, it will collide with the second retransmission of the first VoIP packet. In the conditions of poor radio environment and many retransmissions, such collision possibly occurs per 20 ms, resulting in obviously increased signaling overhead on the PDCCH. It is suggested to configure a new semi-persistent scheduling periodicity to increase the least common multiple of the semi-persistent scheduling periodicity and the HARQ RTT so as to prolong collision interval. However, this configuration will cause the semi-persistent scheduling periodicity and the data arrival interval to be inconsistent, so that the upper layer needs to buffer arrived data for a while till the nearest semi-persistent scheduling periodicity comes, and then transmits the data. The time delay of buffering will increase as time goes on, until the time delay equals to the data arrival interval, then 2 upper layer data packets will be transmitted at a time, this cannot reuse the semi-persistent scheduling UL grant, and a new dynamic scheduling needs to be granted through the PDCCH. With respect to the radio frame of LTE TDD with the length of 10 ms, the frame structure is shown in FIG. 3, in which there are generally 7 configurations for the uplink and downlink sub-frames of a radio frame, as shown in Table 1 and FIG. 4.
TABLE 1Radio Frame Configuration Scheme in the LTE TDD SystemConfig-SwitchurationPointSub-frame Serial NumberNumberPeriodicity01234567890 5 msDSUUUDSUUU1 5 msDSUUDDSUUD2 5 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD610 msDSUUUDSUUD